The present invention relates to a threaded connector for pipes, more particularly for steel pipes which is intended for the petroleum and gas industry and for connecting pipes produced from this connector, of particular importance because of its tight seal against high external pressures.
The present invention relates to a threaded connector for pipes, more particularly for steel pipes which is intended for the petroleum and gas industry and for connecting pipes produced from this connector, of particular importance because of its tight seal against high external pressures.
Pipe connectors used in the petroleum and gas industry are known in which the junction is constituted by an externally threaded male element which screws into an internally threaded female element, the two male and female threads mating with each other. Such connectors are used to produce extraction pipe strings or casing pipe strings for petroleum and gas wells.
Pipe connectors used in the petroleum and gas industry are known in which the junction is constituted by an externally threaded male element which screws into an internally threaded female element, the two male and female threads mating with each other. Such connectors are used to produce extraction pipe strings or casing pipe strings for petroleum and gas wells.
Depending on the severity of the conditions of the petroleum and gas exploitation wells, the basic structure of the connectors described above is completed in known manner by providing them with a variety of types of sealing means such as rings of synthetic material or metallic surfaces which bear on each other.
An example which can be cited is described in European patent EP 0 488 912 which describes a tapered threaded connector provided with a male tapered surface in the zone located after the male thread close to the free end of the male element, and in the corresponding zone of the female element with a corresponding female tapered surface, this pair of male and female surfaces bearing on each other when the connector is in the made up position forming an internal sealing surface against fluid circulating inside the pipes. The connector described in EP 488 912 is also provided with an abutment which enables the two male and female threaded elements to be precisely positioned with respect to each other when making up.
For certain applications, the connectors must resist and remain sealed both to the internal fluid pressure circulating in the pipe and to the external pressure existing outside the pipe. Such a seal is critical for the reliability of the connector when the external pressure is high (for example over 600 bars), whether the fluid concerned is a liquid or a gas or a mixture of the two. In this case, beyond a given pressure the internal sealing surface such as that described in EP 488 912 cannot resist fluid penetration which advances from the exterior to the interior along the thread and can then deform or even break the male lip on which said internal sealing surface is located, and it thus infiltrates into the interior of the pipe.
To overcome this problem, it has been proposed to provide the type of connector described in EP 0 488 912 with a sealing surface located close to the free end of the female element.
French patent FR 77 12851 thus describes a connector provided with an internal sealing surface close to the free end of the male element and with an external sealing surface close to the free end of the female element. It should be tight to internal and to external pressure. However, according to FR 77 12851, each of those two sealing surfaces is associated with an abutment, which renders the function and manufacture of the connector much more difficult. Abnormal deformations can occur when dimensional tolerances are not entirely adhered to or when the makeup torque is too high, which deformations can fundamentally modify the function of the two sealing surfaces and cause them to lose tightness as regards the fluid inside the pipe and the fluid outside the pipe.
Producing such a connector is expensive, firstly because of the machining tolerances required for it to function properly and secondly because of the quantity of material necessary to produce both an internal sealing surface and an external sealing surface, requiring the use of thicker pipes.
The prior art also discloses connectors in which the male and female elements comprise a tapered or straight threading constituted by two radially and axially offset independent threaded zones (such threaded zones can also be termed steps) which are provided with sealing surfaces.
Such is the case in EP 0 767 335 which describes a connector which comprises a tapered threading with two independent radially and axially offset threaded zones, with an internal sealing surface close to the free end of the male element and an external sealing surface close to the free end of the female element. However, because of the situation of the external sealing surface close to the free end of the female element, this sealing surface cannot resist very high pressures as there is not sufficient material at the end of the pipe to keep said surface rigid.
Further, EP 0 149 612 describes a connector which comprises a threading with two radially and axially offset independent threaded zones with different tapers between which a sealing surface is provided constituted by male and female surfaces in bearing contact during makeup, that connector also comprising an internal sealing surface close to the free end of the male element and an oblique abutment at the free end of the male element.
Because of the structure of the two radially and axially offset independent threaded zones, the connector of EP 0 149 612 requires relatively thick pipe walls and because of the corresponding cost and bulk, it is difficult to envisage it being produced in the form of a coupling.
The present invention seeks to provide a threaded pipe connector which, while being tight to external pressure, does not have the disadvantages of the above connectors.
The present invention seeks to provide a threaded pipe connector which, while being tight to external pressure, does not have the disadvantages of the above connectors.
Thus a connector is sought which is tight at high external pressures while remaining tight to internal pressure and which is simple, robust and economical both as regards the quantity of material and the thickness of the pipes which are required, and as regards machining.
The term xe2x80x9crobustxe2x80x9d means a connector which can resist high pressures, for example of the order of 600 bars to 1500 bars, and which is easy to assemble on-site.
The production of a threaded pipe connector has also been sought, which connector differs as little as possible from connectors which already exist, where the threading is constituted by a single threaded zone in contrast to threaded connectors wherein the threading comprises two independent axially and radially offset threaded zones, and which can be produced from such connectors with a single threaded zone without modifying the structure of the assembly.
A connector which has a single sealing means which can be used both against internal pressure and against external pressure has also been sought.
The connector of the invention is intended for the production of pipelines or strings.
Its field of application is not limited to the petroleum and gas industry but extends to any application where the.same types of problems occur or can occur.
A non limiting example is geothermal liquid or vapour water extraction.
The connectors are produced from any metallic materials, for example steel or ferrous or non ferrous alloys in particular with the desired mechanical characteristics and with the corrosion strength required for the envisaged application.
The threaded pipe connector of the invention is of the type comprising a male element disposed at the end of a first pipe and a female element disposed at the end of a second pipe.
The male element comprises an external male threading constituted by a single male threaded zone and the female element comprises a female threading constituted by a single female threaded zone, the male threaded zone corresponding to the female threaded zone such that they can be made up one into the other.
The male and female threading are tapered and a stop means can stop makeup of the connector at a set position.
A sealing means is interposed between the male and female element, which means is constituted by a male bearing surface on the male element and a female bearing surface on the female element, these two bearing surfaces being capable of coming into bearing contact with each other when the connector is made up and being respectively disposed in a globally central zone of the male threaded zone for the male bearing surface and a globally central zone of the female threaded zone for the female bearing surface in which the respective male and female threadings are interrupted.
The term xe2x80x9cglobally central zonesxe2x80x9d of the male threaded zone and of the female threaded zone in which the male and female threadings are interrupted means a zone which is substantially at the mid point along the axis of the connector of the male and female threaded zone or in a portion which extends to either side of the mid point along the axis of the connector of the male and female threaded zone by a length of at most xc2xc of the length along the connector axis of the threaded zone.
Advantageously, the male threaded zone and the female threaded zone will be considered to encompass both perfect threads and imperfect or vanishing or incomplete end threads.
In the following text, this sealing means will simply be termed the xe2x80x9ccentral sealing meansxe2x80x9d, it being understood that this term must not be interpreted restrictively having regard to the information provided.
The stop means which can stop makeup of the male element in the female element in a set position can be constituted either by means linked directly to the threadings or by means which are independent of the threadings.
Since the threadings are tapered, they naturally have an interference fit, and the stop means directly linked to the threadings can be constituted, as is already known, by makeup to a pre-set torque or by two marks, one located on the male element and one on the female element, which coincide at the end of makeup.
Regarding means which are independent of the threadings, the stop means can be an abutment which, in the desired position, opposes continued relative makeup of the male element into the female element.
Depending on the envisaged service conditions for the connector of the invention, the connector may comprise only one single sealing means as described above, the central sealing means, or in addition to this central sealing means it may also comprise a second sealing means.
This second sealing means is advantageously a means which is known per se such as a metal-metal bearing contact ensured by two bearing surfaces respectively disposed one close to the free end of the male element and the other on the corresponding portion of the female element.
The bearing surfaces of the central sealing means can be of any type or form provided that they can come into bearing contact with each other during makeup of the connector.
As an example two cylindrical surfaces can be used, the male bearing surface being of a slightly higher diameter than the diameter of the female bearing surface to ensure an interference fit of the two surfaces when made-up, creating the seal.
It is also possible to use at least one cylindrical surface, the other surface being toric, for example, or of any nature which can bring about an interference contact with the former.
The male bearing surface and the female bearing surface do not necessarily have the same type of geometry.
Advantageously, at least one of the bearing surfaces of the central sealing means, the male surface or the female surface, is constituted by a tapered surface the taper of which is in the same direction as the threading taper but wherein advantageously the angle with respect to the common axis of the male element and the female element is higher than the angle of the thread taper with respect to this axis.
By way of non limiting example, the contact distance between the male and female bearing surfaces of the central sealing means can be in the range 1 to 10 mm.
The threadings of the male and female elements can be of any type, such as for example triangular or trapezoidal API (American Petroleum Institute) threadings, the latter ones being termed xe2x80x9cbuttressxe2x80x9d by the API, world known designation and the use of which is common to the man of art to design said type of threadings.
In the case of a buttress threading, they may have negative load flanks, in particular when associated with an abutment, to enable the threadings to engage together better.
The present invention also relates to a threaded connection for two pipes using the connector of the invention, the structure of which has been described above.
A number of variations are possible.
In a first variation, the connection is integral, each pipe to be connected carrying alternately at each of its ends a male element and a female element of the connector of the invention, as described above.
Thus the integral connection of two pipes is carried out by screwing the male element at the end of a first pipe into the female element at the end of a second pipe.
Depending on the configuration and thickness of the pipes, it may be advantageous to form the female element on the end of a pipe where the external diameter has previously been expanded, the male element being produced on a pipe the end of which can if necessary have been thickened, for example by hot forming.
In a second variation, the connection for two pipes is of the coupled type, i.e., produced using a coupling joining the two pipes, and employs two connectors of the invention, the structure of which has been described above.
In this case, a male element as described above is formed at each pipe end and a female element as described above is formed at each end of a coupling, the two male elements at the two ends of two pipes to be connected being screwed into the two female elements of the coupling.
In this case, the free ends of the two pipes to be connected can, in a first embodiment, come into a bearing relationship with each other inside the coupling at the end of makeup, thus constituting an abutment which can stop makeup at the set position.
In a second embodiment of the coupled connection, the free end of each pipe comes into a bearing relationship with a stop-lug provided in the central portion of the coupling.